Autonomous measuring systems with remote data transmission

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					                                              Measuring system transmits data via
                                              e-mail and collects the measuring
                                              data centrally on a PC

                            Autonomous measuring systems
         with remote data transmission (GSM-2)
                                             by Marcel Gautschi, Dipl. El.-Techniker TS

There has been a need for autonomously operating measu-                 use of mobile radio networks for data transmission. The
ring systems for quite some time, but until now they have               GSM reception coverage is so far advanced and the price of
only been implemented using locally read-out data loggers.              telephone modules and call costs are so low that this is the
However, this meant that the data that was acquired was ne-             cheapest and simplest measurement acquisition method,
ver up to date, and merely provided a historical picture. The           not just for decentralised or extremely remote measuring
measuring devices did not have a continuous function moni-              points, but also easily accessed locations.
toring facility.                                                        The cost of data transmission is a fraction of the cost of per-
                                                                        sonnel for measurement acquisition. Furthermore, this entire
The use of mobile radio networks and the Internet has now               measuring system with GSM transmission is only slightly more
made it possible to create a virtual combination of widely              expensive than a data logger without GSM transmission.
distributed measuring systems in one location, and make                 The cost of transmitting measuring data via e-mail is extre-
use of the acquired data on the spot.                                   mely cheap at the moment. If a prepaid card is used, there
                                                                        are not even any monthly charges.

Modern measuring systems are cheaper                                    Data transmission via e-mail or SMS is the easiest solution to
                                                                        implement in practice, because not much needs to be done
Professional measuring technology has reaped considerable               at the receive end. A normal mobile phone is sufficient for
benefits from the use of components and technology that                 reading out the measuring data (SMS) using PC, or a PC
were originally developed for the large quantities that were            with an Internet connection via which the data can be received
needed for consumable products. A current example is the                by e-mail.

                       - August 2009 -                                                    
                                                                 Keller AG für Druckmesstechnik has therefore developed
                                                                 the GSM-2 module for its water level measuring sensors.
                                                                 The usage locations are almost limitless. Measurements like
                                                                 this used to be carried out manually using an electric contact
                                                                 gauge. A 2-inch diameter pipe embedded in the ground was
                                                                 completely sufficient. However, the measuring frequency
                                                                 was extremely dependent on the accessibility of the measu-
                                                                 ring points and the prevailing weather conditions. In order
Illustration of the GSM-2                                        to equip the existing measuring stations with a measuring
measuring system                                                 system, the GSM-2 module has been designed with a dia-
                                                                 meter that allows it to be inserted into the so-called sounding
Data processing: The PC as a data logger
                                                                 The measuring stations, most of which are located in remote
The heart of the measuring system is the user-friendly and       areas for geographical or hydrographic reasons, do not have
free GSM-2 DataManager software. It collects the measuring       a power connection, of course. In other words a battery-
data, monitors and controls the different measuring stations     operated system with as long a service life as possible is
(GSM-2) and is used to display or automatically process the      required. However, the list of requirements gets longer: the
measuring data, which is stored in a MySQL database.             measuring equipment must be resistant to water and humi-
                                                                 dity, and also be able to withstand short periods of immersi-
The data that is transmitted by the GSM-2 (e-mail/SMS) is        on. Finally, it must be protected against theft and vandalism.
continuously read in by the DataManager and stored in the
It is evident at a glance whether all measuring stations are     Quick and easy installation
operating correctly. In the event of an error, e.g. missing
measuring data, this is shown on the PC screen or the re-        The entire GSM-2 measuring module
sponsible person is notified by SMS or e-mail. Measuring         is simply inserted into the 2-inch dia-
data is converted into the physical quantity that is used at     meter sounding pipe and secured by
the measuring location, and can be displayed in graphical        the level sealing cap. No complicated
format. The measuring station locations are displayed on a       and expensive installation of antenna
map.                                                             with mast and solar panel required!
                                                                 Installed within seconds.
Configuration changes for the individual measuring stations
(GSM-2) are made on the PC. The new configuration is             After installation, the GSM-2 trans-
transmitted by e-mail and received by the relevant GSM-2         mits its configuration with measuring
module.                                                          station name and position to the Data-
                                                                 Manager, which automatically starts
                                                                 to manage the new measuring station
Applications                                                     immediately.

The GSM-2 is suitable for use in locations where no power
supply is available or cables cannot be used. Typical appli-     Facts
cations are: tanks on vehicles or building sites, and ground-
water and waste water level measurements.                         Battery operated (up to 10 years with one battery)

                                                                  Quick and easy installation
GSM-2 for groundwater level measurement
                                                                  Different interfaces for sensors
The monitoring of groundwater levels or the surface levels
of lakes and rivers is a widespread task. It is carried out by    Free software
different state-run institutions and also private water and
energy providers.                                                 Low cost

The DataManager software monitors the
measuring stations and processes the
measurements (graphical display, …)

    Technical details

    The electronics and the battery of the GSM-2 module are
    accommodated in a watertight stainless steel housing with
    an external diameter of 48 mm.                                           Measuring inputs for various sensors and applications

    The upper part, which is designed to be secured in a lockable            In addition to the RS485 interface, via which the pressure
    standpipe sealing cap with antenna for 2” pipes, contains                or water level can be read out with extreme accuracy using
    the antenna and the interface for configuring the measuring              KELLER water level sensors, an air pressure and tempera-
    system. The level measuring sensor is attached to the bot-               ture sensor is installed in the module itself. This makes it pos-
    tom end.                                                                 sible to make water level measurements using the so-called
    Depending on the ambient conditions and the configuration,               AA measuring method (absolute-absolute). The advantage
    the battery operated device can have a service life of more              of this measuring method is that no humidity-sensitive ca-
    than 10 years! The GSM module is simply switched on when                 pillary tube needs to be installed in the cable of the level
    it is needed (i.e. in order to call up incoming configurations or        sensor. This makes the measuring station extremely robust
    send the measuring data or the system configuration).                    and suitable for reliable use in damp and wet environments;
                                                                             not even short periods of immersion cause the measuring
                                        Several level values that have       station to fail.
                                        been measured within a defined
                                        time period and stored (in the       The two voltage inputs (0 – 2.5 V), the SDI12 interface or the
                                        GSM-2) are sent in a single mes-     two digital inputs allow customers to connect applications
                                        sage (e-mail/SMS).                   with all kinds of sensors to the device. From a simple switch
                                                                             contact (digital input) to an expensive and complex water
                                        At the same time, critical events    analysis unit with up to 10 parameters (SDI12 interface).
                                        such as rapid level changes and
                                        levels that exceed maximum or        The connected sensors are optionally supplied with a voltage
                                        minimum limits can be detected       of 12 volts, 5 volts or 3.7 volts by the GSM-2.
                                        in another interval and additional
                                        messages transmitted in the form
                                        of e-mail or SMS alarms. The
                                        periodic transmission of system
                                        information containing current
                                        levels, battery capacity, antenna
                                        signal strength and other informa-
                                        tion can also take place.

GSM-2 measuring
module with level

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